1. Technical Field
The present invention relates to an apparatus for forming an image without a cleaner (referred to as "cleanerless image forming apparatus") and particularly to a cleanerless image forming apparatus which is used in facsimile machines, copy machines or the like.
2. Background Art
Generally in a conventional cleanerless image forming apparatus, an exposing unit forms an electrostatic latent image on a photosensitive drum, a developing unit feeds a toner over the electrostatic latent image and a transfer unit transfers the toner onto a recording sheet. The toner remaining on the photosensitive drum after the transfer operation is uniformly scattered around over the photosensitive drum by a memory removing member. The memory removing member is usually a conductive brush and located to face the photosensitive drum. Since the scattered toner still stays on the photosensitive drum, this toner is collected by the developing unit with an electrostatic attracting force while the developing unit feeds the toner onto the photosensitive drum. In this manner, the cleanerless image forming apparatus does not have a separate device exclusively used for cleaning the toner and the developing unit performs both the developing operation and the cleaning operation.
However, upon scattering the toner, if a large amount of toner adheres to the memory removing member, the toner scattering ability of the memory removing member will drop and the developing unit cannot collect the toner sufficiently. As a result, a certain amount of the above-mentioned remaining toner still remains on the photosensitive drum and is printed on the recording sheet as an afterimage during the next image forming operation (or printing operation).
Regarding this problem, another conventional cleanerless image forming apparatus performs the cleaning of the memory removing member, i.e., the toner removing, before each image forming process. In this toner removing operation, the photosensitive drum is charged to a certain plus voltage by the transfer unit while the voltage application to the memory removing member is cut to make the memory removing member voltage zero. The voltage difference between the photosensitive drum and the memory removing member produces the electrostatic attracting force which pulls the toner off the memory removing member. The pulled off toner adheres to the photosensitive drum and it is collected by the developing unit later.
However, since the above described image forming apparatus conducts the cleaning of the memory removing member upon receiving the print instruction from an operator, the printing operation does not start until the cleaning operation is completed. In other words, there is a time lag (or time loss) between the print instruction from the operator and an actual printing.
In addition, the cleaning of the memory removing member is carried out upon the print instruction from the operator and this means that the memory removing member is not cleaned until the next printing instruction comes. Thus, the toner is kept on the memory removing member until then. If a long period of time elapses before the next printing command, the toner may be solidified on the memory removing member and it may become difficult to peel the toner off the memory removing member.
Moreover, if the jamming occurs and the image forming operation is interrupted, a large quantity of toner is left on the photosensitive drum without being transferred to the recording sheet. After eliminating the jamming, if the image forming operation is restarted without any special care, the above mentioned large quantity of toner adheres on the memory removing member and the toner scattering ability of the memory removing member is deteriorated. Consequently, sufficient charging and exposing cannot be expected and the printing quality will drop.